Sialic acids comprise a varied group of nine-carbon amino sugars widely distributed among mammals and higher metazoans. Commensal and pathogenic bacteria that colonise heavily sialiated niches (e.g. the mammalian respiratory tract and gut) can scavenge sialic acids from their surrounding environment. Scavenged sialic acid is used as a carbon, nitrogen and energy source, or to evade the host immune response by decorating their outer surfaces in sialic acid. Bacterial sialic acid membrane protein transport systems have been identified that belong to the tripartite ATP-independent periplasmic transporters, ATP-binding cassette, major facilitator superfamily and sodium solute symporter transport systems. Here we report the 1.95 Å resolution crystal structure of a specific sialic acid sodium solute symporter, SiaT, in its outward-open conformation. The structure of SiaT was determined in complex with sodium and sialic acid bound, providing insight into how this transporter mediates the movement of sialic acid across the membrane.